1. Field of Invention
The present invention is directed to a fastener driving tool with a novel lockout mechanism to prevent firing in a fastener-empty condition.
2. Description of Related Art
A fastener driving tool typically has three regions: a back end enclosing a firing mechanism, a front end comprising a muzzle and a magazine, and an intermediate region comprising a tool body. The typical tool includes a tool body and a barrel housed coaxially within the tool body. The barrel contains and guides a piston, driven by a firing mechanism activated by a trigger. A buffer assembly in the barrel stops the flight of the piston. A muzzle, housed within a muzzle housing, extends forward from the tool body and is displaceable from an extended position into a ready-to-fire position when pressed against the receiving substrate.
Fastener driving tools desirably include a contact pressure safety feature assuring that the firing mechanism fires only when the muzzle is pressed against the receiving substrate. When pressed against the receiving substrate, the muzzle displaces into ready-to-fire position and enables the firing mechanism to fire when the trigger is pulled.
In some fastener driving tools, a magazine is coupled to the muzzle in order to minimize fastener loading time. Multiple fasteners loaded into the magazine allow the user to fire multiple fasteners before needing to reload the tool. The magazine contains a follower that biases the fasteners toward the muzzle for driving by the piston into receiving substrate.
The tool should not fire when there are no fasteners in the magazine, known as fastener-empty condition, because the piston can damage the tool. Without the resistance of a fastener being driven into the receiving substrate, the flight of the piston can damage the buffer assembly as well as the follower.
A previous tool, as disclosed in U.S. Pat. No. 4,809,898, prevents firing during fastener-empty condition by providing a stop shoulder on a back surface of a follower which occupies a space between the magazine and the muzzle housing. The stop shoulder prevents the magazine from moving toward the back end of the tool, thus prohibiting the muzzle from displacing far enough to establish the ready-to-fire position.
What is needed is a direct way to prohibit the muzzle from moving into the ready-to-fire position during fastener-empty condition.